Resistance spot welding method

Abstract

Provided is a resistance spot welding method capable of efficiently generating a nugget that is as large as possible while reducing the occurrence of spatter. The resistance spot welding method includes: placing on top of one another at least two steel plates including a plating layer of zinc as a main component or an Al—Si plating layer; sandwiching the at least two steel plates between a pair of electrodes; and performing preliminary current application between the pair of electrodes and then performing main current application. The resistance spot welding method performs the preliminary current application so as to include a current application pattern in which a current value of a welding current at a current application start time of the preliminary current application is set as a maximum value, and the current value sequentially decreases stepwise from the maximum value.

1 . A resistance spot welding method, comprising:
 placing on top of one another at least two steel plates including a plating layer of zinc as a main component or an Al—Si plating layer;   sandwiching the at least two steel plates between a pair of electrodes; and   performing preliminary current application between the pair of electrodes and then performing main current application, such that the steel plates that are adjacent to each other are melted and joined together,   wherein the preliminary current application is performed so as to include a current application pattern in which a current value of a welding current at a current application start time of the preliminary current application is set as a maximum value, and the current value sequentially decreases stepwise from the maximum value along with a lapse of a current application time from the current application start time.   
     
     
         2 . The resistance spot welding method according to  claim 1 ,
 wherein   the stepwise current application pattern is composed of multiple combinations of the current value and the current application time for the current value, and   each of the combinations of the current value and the current application time for the current value forming the stepwise current application pattern is a combination of an upper limit current value that can reduce occurrence of spatter and an upper limit current application time that can reduce occurrence of spatter during current application of the upper limit current value.   
     
     
         3 . The resistance spot welding method according to  claim 2 ,
 wherein   through the preliminary current application, a nugget is generated in a boundary portion between the steel plates that are adjacent to each other and also an alloy layer surrounding the nugget is generated, the alloy layer being made of a material of the plating layer and a material of a base material of the steel plates, and   each of the combinations of the stepwise current application pattern is a combination in which a ratio of an outer dimension of the alloy layer to an outer dimension of the nugget in a direction along the steel plates has a reference value in a range of 1.2 to 1.5.   
     
     
         4 . The resistance spot welding method according to  claim 1 ,
 wherein   a preliminary current application period in which the preliminary current application is performed includes a first period starting from the current application start time and a second period starting after the first period,   the current application pattern of the preliminary current application in the first period is the stepwise current application pattern, and   the current application pattern of the preliminary current application in the second period is an upslope current application pattern in which the current value gradually increases from the current value at the first period end time along with a lapse of the current application time.   
     
     
         5 . The resistance spot welding method according to  claim 1 , wherein the current application pattern of the main current application is a current application pattern in which the current value at a time when the preliminary current application ends is maintained constant from the time when the preliminary current application ends to a time when the main current application ends.